What are LH and FSH?
LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone) are gonadotropins , hormones produced by the pituitary gland that act as the control signals for the gonads. In men, LH signals the Leydig cells in the testes to produce testosterone, while FSH signals the Sertoli cells to support sperm production. In women, LH and FSH work in a coordinated cycle to regulate ovulation, and to direct the ovaries to produce estrogen and progesterone at the right times.
The critical clinical value of testing both LH and FSH together is diagnostic localization: they tell you where in the hormonal axis a problem lives. A man with low testosterone, low LH, and low FSH has a problem originating in the pituitary or hypothalamus (secondary hypogonadism) , the brain is not sending adequate signals to the gonads. A man with low testosterone but high LH and FSH has a problem in the testes themselves (primary hypogonadism) , the brain is signaling loudly, but the gonads are not responding. This single distinction determines which research approaches are mechanistically relevant and which are not.
What do the numbers mean?
FSH Men: 2–8 IU/L
LH Women (follic.): 2–9 IU/L
FSH Women (follic.): 3–10 IU/L
FSH Men: 1.5–12.4 IU/L
(Women: highly variable by cycle phase)
Low LH/FSH + Low T = Secondary
LH and FSH interpretation is strongly context-dependent , always interpret alongside testosterone, estradiol, and SHBG. For women, cycle phase at time of draw is critical; values during menopause and perimenopause follow entirely different patterns.
Why this marker matters before peptide research.
LH and FSH are the detective markers of the HPG (hypothalamic-pituitary-gonadal) axis , they locate the problem. For researchers considering GH secretagogue protocols, LH and FSH provide important context because the GH axis and HPG axis interact. GH elevation influences LH pulsatility and downstream testosterone production. A researcher whose low testosterone reflects secondary hypogonadism (inadequate pituitary signaling) is working with a different biological picture than one whose testosterone is low despite normal LH and FSH. Understanding baseline LH and FSH allows accurate interpretation of any hormonal changes that occur during a GH protocol.
For reproductive peptide research, LH and FSH are mechanistically central. Kisspeptin-10 stimulates the hypothalamus to release GnRH (gonadotropin-releasing hormone), which directly triggers LH and FSH release from the pituitary , LH is the immediate downstream marker of Kisspeptin-10 activity. Measuring baseline LH before a Kisspeptin-10 protocol establishes what the peptide is working with and provides the comparison point needed to evaluate whether a biological effect occurred. Without a baseline, there is no reference.
Extremely elevated FSH in men , particularly above 20–30 IU/L , is associated with primary testicular failure and significantly reduced fertility. This context is critical before any reproductive or testosterone-adjacent research protocol, as it indicates the fundamental gonadal machinery may be impaired in ways that peptide-based interventions cannot address.
How to get this test.
Where to order
Standard blood draw at LabCorp, Quest Diagnostics, or through a physician. Often included in comprehensive hormone panels. Available via some direct-to-consumer services, though a physician order is commonly required for this combination.
How to prepare
Morning draw preferred for men , LH follows a pulsatile pattern, so morning values provide the most consistent baseline. For women, cycle phase matters significantly , follicular phase (days 2–5) provides the most standardized reference values. Note cycle day on the requisition.
What to ask for
"LH and FSH" , order both simultaneously. Always interpret alongside total testosterone, free testosterone, estradiol, and SHBG. The combination of all five creates the complete sex hormone axis picture needed for any hormonal research context.